Fluid-actuated servomechanism with multiple inputs



Jan. 5, 1965 R. L. CARSON 3,164,064

FLUID-ACTUATED SERVOMECHANISM WITH MULTIPLE INPUTS Filed Nov. 7, 1963 Fig. l.

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FLUID-ACTUATED SERVOMECHANISM WITH MULTIPLE INPUTS Filed Nov. 7, 1963 3 Sheets-Sheet 2 f/vvenfor Robe/"7 L. Carson by w. Z. @Wr/a,

H/s Affor/jey R. L. CARSON Jan. 5, 1965 FLUID-ACTUATED SERVOMECHANISM WITH MULTIPLE INPUTS Filed Nov. 7, 1963 3 Sheets-Sheet 5 [m/enfor Robe/"7 L. Carson /-//'s A ffO/"ney United States PatentOflfice 3,154,064 Patented Jan. 5, 1965 3 164,964 FLUID-AQTUATED ERVGMECHANISlt/l WETH MULTIPLE INPUT Robert L. Carson, Scntia, N.Y., assignor to General Eiectric Company, a corporation of New York Filed Nov. 7, 1%3, Ser. No. 322,193 6 mamas. ((11. 9ll--20) This invention relates to an improved fluid-actuated servomechanism having several input signals, such as to a number of servo valves controlling a fluid-responsive member, wherein one of the input signals is capable of overriding all of the others to control the action of the member in a predetermined manner. More particularly, the invention relates to an improved arrangement for controlling a hydraulic double-acting servomotor from two or more hydraulic servo valves, connected so that any one f the servo valves can override all of the others and exercise sole control over the servomotor.

' Various overriding schemes have been suggested for fluid-actuated servomechanisms, so that only a selected one of several input movements will actually exercise control over the fluid-responsive member at any given time. These input movements are applied to the movable members of servo valves or pilot valves which control the flow of fluid to and from a servomotor. It may be desired that, out of multiple input movements, the least movement should control the member, all other input movements being ignored by the servomechanism, or alternately, it may be desired that the greatest movement of an input member exercise control over the controlled member, all lesser inputs being ignored by the servomechanism. This is often spoken of as overriding, i.e. one input motion receives a clear preference over all other input motions to exercise soie control.

Various overriding schemes of a mechanical nature have been employed with such servomechanisms. Also, it has been proposed in the past that several servo valves arranged in series might provide overriding features for a single-acting (spring or gravity returned) servomotor. Single-acting servomotors are unsatisfactory for some applications, however, and it has been desired for some time that an arrangement be devised, whereby a selected one of several hydraulic servo valves might override all others and exercise control over a double-acting servomotor.

Accordingly, one object of the present invention isto provide an improved fluid-actuated double-acting servomechanism with multiple inputs, arranged so that any one of the inputs will override all of the others in a predetermined manner to exercise control over the servomechanism.

Yet another object of the invention is to provide an improved arrangement for a hydraulic double-acting servomechanism controlled by two or more servo valves, wherein the servo valve receiving either the least or greatest movement in a given direction will override all of the other servo valves.

Another object of the invention is to provide an improved hydraulic control mechanism receiving multiple position inputs to control an output member which also operates a feedback linkage to the input members, wherein one of the input members will override all of the others when moved in a predetermined direction.

Briefly stated, the invention is practiced by employing two or more servo valves controlling the flow of fluid to a double-acting servomotor, together with mechanical feedback linkage. When the movable members of the valves are all to one side of the neutral position, the connections are such that the oil supply is connected in series through the servo valves to one side of the servomotor piston, while the other side of the servomotor piston is connected in series through the servo valves to the drain in the same sequence as previously. When the connections are made thus, the servo valve with the movable member displaced the greatest extent to the other side of the neutral position will override all others.

The organization and operation of the invention, together with further objects and advantages thereof, may best be understood by reference to the following description taken in connection with the accompanying drawing, in which:

FIG. 1 is a schematic diagram of a prior art hydraulic servomechanism with double-acting servomotor and restoring linkage to the servo valve,

FIG. 2 is a schematic diagram of a hydraulic servornechanism according to the invention with two servo valves connected to a double-acting servomotor,

FIG. 3 is a schematic diagram of an arrangement similar to FIG. 2 and operating in the same manner, but employing different type servo valves,

FIG. 4 is a schematic diagram of an arrangement similar to FIG. 2, but arranging for overriding of the servo valves in a different manner than in FIG. 2, and

FIG. 5 is a schematic diagram of a double-acting servomotor having four servo valves arranged according to the invention.

Referring to FIG. 1 of the drawing, a conventional prior art hydraulic servomechanism is illustrated, which positions an output member 1 in response to the input movements imparted to the lefthand end of floating lever 2. An input movement in the direction of the arrow given to lever 2 Will move member]. a proportional distance in the direction of its arrow. The left-hand end of lever 2 is moved by a suitable mechanism (not shown) to operate the stem 3 of a hydraulic servo valve 4. Sleeve 5 of servo valve 4' has an inlet port s connected to a source of hydraulic fluid under pressure (not shown), two control ports 7, 8 covered by the lands of servo valve stem 3:, and two drain ports 9, iii. I I V The output member 1 is the stem of a hydraulic piston 11 disposed in a cylinder 12, the piston and cylinder together comprising a hydraulic servomotor designated generally as 12. Cylinder 12 has ports 14, 15 connected to the chambers above and below piston 11 respectively. The servo valve control port 8 is connected to servomotor port 14 by a pipe or conduit 16. Similarly, servo valve control port 7 is connected to servomotor port 15- by conduit 17.

A feedback or restoring linkage for returning stem 3 of the servo valve to its neutral position as output member 1 seeks its new position is comprised of a link 18 pinned to a lever 19 on one end thereof. A second link 20 is pivotably connected between lever 19 and the free end of floating lever 2. It remains to note that drain ports 9, 10 of the servo valve 4 are connected to a suitable exhaust or drain passage for returning spent hydraulic fluid to the source;

Although the operation and arrangement of the servomechanism of FIG. 1 are well known, its operation will be described briefly in a slightly diiferent manner which will facilitate a better understanding of the invention to be described. When servo valve stem 3 is lowered, it provides. communication between a first pairof ports 7, 9-and between a second pair of ports 6, 8. When it is raised, it provides communication between a third pair of ports 6, 7 and between a fourth pair of ports 8', 10. Although it will be noted that inlet port 6 is common'to the first and fourth pairs of ports-mentioned above, a better understanding of the invention tobe described may be had by; considering each of the servo valves as connecting two pairs of ports together when the stem is in a counterclockwise.

position to one side of neutral or no-flow and connecting two other pairs of ports together when the stem is to the other side of neutral. Although the constructional details of servo valves may vary, this principle of operation is always the same, as will be shown.

Referring now to FIG. 2 of the drawing, two four-land hydraulic servo valves designated A and B are arranged to control the supply of fluid to a double-acting servomotor 13. In FIG. 2, as well as in the remaining figures, the same reference numerals have been retained for the servomotor and main restoring linkage elements 1%, 19, since these function in the same'manner as in FIG. 1. Servo valve A has an input member 21 pivotably connected to the servo valve stem 22 and also pivotably connected to a restoring link 23 attached to lever 19. Similarly, servo valve B has an input member 24 connected to the servo valve stem 25 and to a restoring link 26.

When stem 22 is in a raised position, it connects a first pair of ports 27, 28 and a second pair of ports 29, 30. When it is in a lowered position, it connects a third pair of ports 28, 31 and a fourth pair of ports 27, 29.

' Similarly, when stem 25 of servo valve B is in a raised position, it connects a first pair of ports 32, 33 and a second pair of ports 34, 35. When it is in a lowered position, it connects a third pair of ports 33, 36 and a fourth pair of ports 32, 34. A conduit 37a connects ports 28, 32; a conduit 37b connects ports 33, a conduit 38a connects ports 14, 29; and a conduit 38b connects ports 30, 34. Hydraulic fluid is furnished from a pressurized source to port 27 of servo valve A, and the remaining ports 31, 35, 36 are connected to a suitable drain.

By tracing the flow of hydraulic fluid when both valve stems 22, are in a raised position, it will be seen that fluid flows in series through servo valves A, B starting at port 27 through port 28, conduit 37a, port 32, port 33, conduit 37b, and port 15 to the lower side of the piston 11. Return fluid from the top of cylinder 12 flows from port 14 in series through the servo valves in the same sequence (i.e. A and then vB) via conduit 38a, port 29, port 30, conduit 38b, port 34, port to the drain.

It will be observed that the fluid, therefore, flows through servo valves A, B in series to the servomotor and returns in the same sequence through the servo valves A, B in series to the drain. If, for example, the stems of both servo valve A and B are elevated and the stem of servo valve B is then lowered toward the neutral position shown in the drawing, servo valve B has unrestricted control over ingress and egress of fluid to servomotor 13. Servo valve A serves merely as a conduit means for routing fluid to and from servo valve B.

If, for example, servo valve B is lowered below neutral and servo valve A is raised above neutral, supply fluid flows in sequence from inlet 27 through 28, 37a, 32, 34, 38b, 30, 29, 38a, 14 to the top of piston 11. Discharge fluid flows from port 15, through 37b, 33, 36 to the drain. The movement of piston 11 is downward. It will be observed that servo valve B, which was moved downward, is in sole control, since it has overridden the upward movement of servo valve A (which requested an upward movement of piston 11) The piston 11 will move downward rotating lever 19 clockwise and floating levers 24, 21 When servo valve stem 25 of valve B is restored to a neutralposition, the downward movement of piston 11 will stop. It will be observed that what is a restoring movement to servo valve B merely serves to further displace servo valve A from neutral.

In the arrangement shown in FIG. 2, the input member which calls for the lower position of piston 11, be it input member 21 of servo valve A or input member 24- of servo valve B, will always be in sole control and override the piston position called for by the other servo valve.

It will beobserved in analysis that there are occasions when the servo valve not in control (i.e. in FIG. 2 the valve with the higher input) will pass through a neutral position, even though it is not controlling. This does not place that servo valve in control and halt the piston, since this is a transient phenomenon. Leakage past the valve lands and inertia of the members will cause the restoring linkage to move the servo valve stems through these discontinuities.

FIG. 3 illustrates a modified arrangement, in which the left-hand servo valve is designated C and the righthand servo valve D. This modification is shown to illustrate that the constructional details of the servo valves may be quite different and still be used to practice the invention. The arrangement of FIG. 3 may be preferable, in that straight interconnections may be employed between ports, and the valves can be machined easily in a single block.

Servo valve C has a four-land stem 40. However the ports are reversed from the previously discussed servo valve A so that there is a common discharge port in the center rather than a common supply port. Valve stem 41 of servo valve D is a three-land stem.

When stem 40 is raised above neutral, it connects a first pair of ports 43, 46 and a second pair of ports 44, 45. When stem 40 is lowered, it connects a third pair of ports 43, 44 and a fourth pair of ports 45, 47.

Similarly, when stem 41 of servo valve D is raised, it connects together with a first pair of ports 48, 49 and a second pair of ports 58, 51. When stem 41 is lowered, it connects together a third pair of ports 49, 52 and a fourth pair of ports 48, 50. Summarizing, when the stems of both servo valves C, D are raised, they provide communication between first and second pairs of ports in each valve.

The interconnecting conduits are 53a, 5315 which serve to connect in series the first pairs of ports of servo valves C, D in sequence with port 15 of servomotor 13. Similarly, conduits 55a, 55b serve to connect in series the second pairs of ports in each of the servo valves C, D in the same sequence to the drain.

The operation of the arrangement shown in FIG. 3 is exactly the same as in FIG. 2. The input member 21, 24 which calls for the lower position of piston 11 will be in control of the piston and the restoring linkage will operate to restore the controlling or lowermost servo valve stem to a neutral position.

In FIG. 4, another modification is illustrated using two three-land servo valves E, F having input members 21, 24 and restoring links 23, 26 respectively. In the modification of FIG. 4, the hydraulic connections are arranged so that whichever input member 21, 24 which calls for the higher position of piston 11 overrides the other noncontrolling servo valve.

Servo valve E has a stem 57 which, when lowered, connects a first pair of ports 58, 59 and a second pair of ports 60, 61. When servo valve stem 57 is raised, it connects a third pair of ports 59, 62 and a fourth pair of ports 58, 61.

Similarly, servo valve F has a stem 63 which, when lowered, connects a first pair of ports 64, 65 and a second pair of ports 66, 67. When it is raised, it connects a third pair of ports 65, 68 and a fourth pair of ports 64, 66.

Summarizing for FIG. 4, when the stems of both servo valves E and F are lowered, the provide communication between first and second pairs of ports in each valve. This is in contrast to the arrangements of FIGS. 2 and 3, wherein the first and second pairs of ports were defined when the stems were above, rather than below, neutral position. In FIG. 4 the servo valve having the higher input movement will override the other.

When the stems 57, 63 are lowered, hydraulic fluid flows in series through servo valves E, F to the servomotor 13 through the aforesaid first pair of ports in each servo valve by means of conduits 69a, 6%. Discharge fiuid from below piston 11 flows in series through the second pairs of ports in the same servo valve sequence to the drain by means of conduits 70a, 7%.

In the operation of the arrangement shown in FIG. 4,

stages i calling for upward movement of the piston and the stem trols the movement.

FIG. illustrates that the invention is not limited to only two controlling servo valves. Four servo valves are shown designated G, H, I, I with input levers 72, 73, 74, 75 respectively, and stems 76, 77, 78, 79 respectively. The arrangement of FIG. 5 is connected to operate similar to FIGS. 2 and 3, so that the lowermost servo valve stem exercises sole control over the piston 11, and overrides whatever movements of the piston might be called for by the remaining servo valves. Stem 76, when raised, connects a first pair of ports 80, 31 and a second pair of ports 82, 83. When lowered it connects a third pair of ports 31, S4 and a fourth pair of ports 80, 82. The remaining servo valves H, I, I have reference numbers supplied to the ports in like manner. The first pairs of ports for the remaining valves are 85-86, 90-91, and 95-96. The second pairs of ports for the remaining valves are 87-88, 92-93, 97-98. Fluid flows in series from the oil supply through the first pairs of ports in each servo valve in order to the lower side of piston 11 via conduits lfitla, 100b, 1900, 160d. Fluid drains from the upper side of piston 11 through the second pairs of ports in series in the same servo valve sequence through conduits 101a, 101b, 101e, 101a.

The operation of FIG. 5 is the same as that of FIG. 2. The lowermost servo valve stem will exercise control over the servomotor and override the dictates of higher positioned servo valve stems. As an example, suppose that stems 76, 77, 79 of valves G, H, J respectively are raised and stem 78 of valve I is lowered. Fluid flows in sequence through 80, 81, 100a, 85, 86, 9%, 92, 101a, 88, 87, 191b, 83, 82, 101a, 14 to the upper side of piston 11. Return fluid flows through 199d, 96, 95, 109C, 91, 94 to the drain. The piston 11 will move downward until stem 78 of valve I is raised by the restoring linkage to its neutral position.

The principle of operation of the various modification shown is the same. A direction of movement of the servo valve stems which is to be overriding is selected. In FIGS. 2, 3 and 5 this direction is downward, while in FIG. 4 it is upward.

Then the hydraulic connections are made so that when the servo valve stems are all displaced to the side of neutral which is to be the non-overriding direction, i.e. upward in FIGS. 2, 3 and 5 and downward in FIG. 4, the fluid will flow in series through first pairs of ports in each of the servo valves in sequence to the servomotor. Additional conduits are supplied so that the fluid flows in series through the second pairs of ports in the servo valves in the same sequence as before and to the drain. If the conduits between servo valves and servomotor are arranged as described above, they will be correctly arranged for practicing the invention. Restoring linkage is then employed so that when any of the servo valve stems is moved toward the overriding direction, resulting movement of the servomotor will return it to neutral position.

The foregoing described invention allows any practical number of hydraulic servo valves to control a double acting servomotor by insuring that only one of the servo valves, i.e., that in the most extreme direction of overriding movement will exercise control of the servomotor. The arrangement is, of course, not limited to hydraulic devices but may be used with any fluid-actuated device such as a pneumatic system( Also, as seen in the modifications, the particular type and construction of controlling servo valve selected does not limit the versatility of the invention.

Other modifications of the inventionwill occur to those skilled in the art, and while several modifications of the invention have been described herein, it is, of course, intended to cover in the appended claims these and all such additional modifications as fall within the true spirit and scope of the invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A fluid-actuated servomechariism with'multiple control means comprising:

a servomotor with a double-actingfluid-resporisive movable output member,

a source of fluid under pressure,

a plurality of servo valves controlling admission of fiuid to said servomotor, each'of said valves having a movable stem member arranged to provide communication between first and second pairs of ports when in a first position to one side of a neutral position and to provide communication between third and fourth pairs of ports when in a second position to the other side of said neutral position,

a plurality of first conduits connecting said valves in series flow relation through each of said first pairs of ports from said source to said servomotor, and

a plurality of second conduits connecting said valves in the same sequence through each of said second pairs of ports from said servomotor to drain.

2. A hydraulic servomechanism with multiple control means comprising:

a hydraulic servomotor with a double-acting fluidresponsive movable output member,

a source of hydraulic fluid under pressure,

means receiving spent hydraulic fluid for return to the source,

a plurality of servo valves controlling admission of fluid to said servomotor, each of said valves having a movable stem provided with lands arranged to block substantial fluid flow in a neutral position and to provide communication between first and second pairs of ports when in a first position to one side of said neutral position and to provide communication between third and fourth pairs of ports when in a second position to the other side of said neutral position, at least one port in each pair being common to another pair of ports,

a plurality of first conduits connecting said valves in series flow relation through each of said first pairs of ports from said source to said servomotor,

a plurality of second conduits connecting said valves in series flow relation through each of said second pair of ports from said servomotor to said fluidreceiving means, the sequence of connection between the valves being the same with both the first and second conduits, and

linkage means connected between the output member and the valve stems and arranged to move said valve stems simultaneously in a direction which will restore the fluid-controlling valve stem to a neutral position.

3. The combination according to claim 2, wherein at least one of said servo valves is a four-land sleeve valve with an oil supply port in the center thereof common to the first and fourth pairs of ports.

4. The combination according to claim 2, wherein at least one of said servo valves is a four-land sleeve valve with an oil supply port at either end thereof and having a center port common to said second and third pairs of ports. r

5. The combination according to claim 2, wherein there are two servo valves, the first being a four-land I sleeve valve with supply ports at either end thereof and acomr'non center discharge port and the second valve "being a three-land sleeve valve with a common center inlet port and drain ports at either end thereof.

6. A hydraulic servomechanism with multiple controlling means comprising:

a double-acting hydraulic cylinder with a movable piston disposed therein, a source of hydraulic fluid under pressure, vmeans receiving spent fluid for return to said source, a plurality of sleeve servo valves controlling the admission of fluid to said servornotor, each of said valves having a valve stem with lands arranged to block substantial fluid flow therethrough when in a neutral position and to provide communication between first and second pairs of ports when in a first position on one side of the neutral position and to provide communication between third and fourth pairs of ports when in a second position to the other side of said neutral position, each of said pairs having a port common to another pair,

a plurality of first conduit means connecting said valves in series flow relation so as to provide communication between said source and one side of said piston through the valves in a given sequence when all of the stems are in the first position,

a plurality of second conduits connecting said valves in series flow relation so as to provide communication from the other side of said piston to the fluid-receiving means through the valves in the same sequence when all of the stems are in the first position, and

restoring linkage means connected to move all of said valve stems simultaneously in a direction so as to restore a selected one of the stems toward a neutral position when said selected stem is displaced more toward said second position than any other stem.

References Cited in the file of this patent UNITED STATES PATENTS 2,992,631 Fallows July 18, 1961 

1. A FLUID-ACTUATED SERVOMECHANISM WITH MULTIPLE CONTROL MEANS COMPRISING: A SERVOMOTOR WITH A DOUBLE-ACTING FLUID-RESPONSIVE MOVABLE OUTPUT MEMBER, A SOURCE OF FLUID UNDER PRESSURE, A PLURALITY OF SERVO VALVES CONTROLLING ADMISSION OF FLUID TO SAID SERVOMOTOR, EACH OF SAID VALVES HAVING A MOVABLE STEM MEMBER ARRANGED TO PROVIDE COMMUNICATION BETWEEN FIRST AND SECOND PAIRS OF PORTS WHEN IN A FIRST POSITION TO ONE SIDE OF A NEUTRAL POSITION AND TO PROVIDE COMMUNICATION BETWEEN THIRD AND FOURTH PAIRS OF PORTS WHEN IN A SECOND POSITION TO THE OTHER SIDE OF SAID NEUTRAL POSITION, A PLURALITY OF FIRST CONDUITS CONNECTING SAID VALVES IN SERIES FLOW RELATION THROUGH EACH OF SAID FIRST PAIRS OF PORTS FROM SAID SOURCE TO SAID SERVOMOTOR, AND A PLURALITY OF SECOND CONDUITS CONNECTING SAID VALVES IN THE SAME SEQUENCE THROUGH EACH OF SAID SECOND PAIRS OF PORTS FROM SAID SERVOMOTOR TO DRAIN. 